1. Field of the Invention
This invention relates to the polymerization of oligomers of polydiorganosiloxane in the presence of reinforcing filler using trifluoromethane sulfonic acid as catalyst.
2. Description of the Prior Art
Silicone polymer-filler mixtures have been used as electrical insulation greases and as precursors in the production of silicone elastomers. A customary method of producing these mixtures has been mechanically mixing the selected filler into a polymer of the desired viscosity.
Ostrozynski, in U.S. Pat. No. 3,477,988, issued Nov. 11, 1969, teaches that low molecular weight diorganocyclosiloxane and silica filler can be mixed together, then polymerized by a base-catalyzed rearrangement in the presence of a promoter to yield a highly viscous, opaque substance resembling grease. His Example 18 teaches that mixed cyclic dimethylsiloxanes, fumed silica filler, and potassium silanolate catalyst do not polymerize without hexamethylphosphoramide promoter. Ostrozynski states at col. 10, lines 43-48, that efforts to produce filled silicone polymers by rearranging low molecular diorganocyclosiloxane polymers in the presence of high surface area silica fillers has been successful when acidic catalysts were employed. He teaches nothing further concerning the polymerization with acidic catalysts.
Buchner et al., in British Pat. No. 1,325,654, published Aug. 8, 1973, disclose a process for manufacture of a mixture of a high molecular weight linear organopolysiloxane with an acidic or neutral filler. They mix together a low molecular weight diorganocyclosiloxane, filler, and at least 0.05% of the weight of the siloxane of anhydrous perfluoroalkane sulfonic acid. The low molecular weight diorganocyclosiloxane can be mixed with low molecular weight linear polydiorganosiloxane. The temperature of polymerization is below 50.degree. C. They teach that higher temperatures are disadvantageous in that polymerization only reaches a moderate degree, for example, up to an oil of about 1000 centipoise, if the initiator is neutralized at the temperature employed. They further teach that if the neutralization before cooling is omitted, an unusable gel is obtained.